Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, advantageously applicable to an image pickup apparatus that uses an image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera, or to an image pickup apparatus that uses a silver-halide film.
Description of the Related Art
In recent years, a zoom lens for use as an image pickup optical system in an image pickup apparatus is desired to have a small overall lens length, a high zoom ratio, and a high resolving power. As a zoom lens meeting these demands, a positive lead type zoom lens is known, which has a lens unit having a positive refractive power at a position closest to an object side.
Japanese Patent Application Laid-Open No. 2011-145565 discloses a four-element zoom lens consisting of, in order from an object side to an image side, first to fourth lens units having positive, negative, positive, and positive refractive powers, respectively. For zooming, the second lens unit and the fourth lens unit move with the first lens unit not moving. For focusing, the fourth lens unit moves.
Japanese Patent Application Laid-Open No. 2012-88603 discloses a four-element zoom lens consisting of, in order from the object side to the image side, first to fourth lens units having positive, negative, positive, and positive refractive powers, respectively. For zooming, the second, third, and fourth lens units move. For focusing, the fourth lens unit moves. Japanese Patent Application Laid-Open No. 2007-212926 discloses a five-element zoom lens consisting of, in order from the object side to the image side, first to fifth lens units having positive, negative, positive, positive, and negative refractive powers, respectively. For zooming, the second and fourth lens units move with the first lens unit not moving. For focusing, the fourth lens unit moves.
It is typically easy to increase the zoom ratio of a positive lead type zoom lens. However, when the zoom ratio is increased, aberration variation increases in a range from a wide-angle end to a middle zoom position.
In order to obtain a zoom lens offering a high zoom ratio and high optical performance, it is important to appropriately determine the refractive power and configuration of each lens unit, or especially, the third lens unit.